Ultraviolet sensors have been widely used as ultraviolet detection devices such as germicidal lamps for killing bacteria floating in the air or in water and ultraviolet irradiation devices, and also expected to be applied to optical communication devices in recent years.
As this type of ultraviolet sensor, sensors using diamond semiconductors or SiC semiconductors as a sensing material have been known conventionally. However, these diamond semiconductors and SiC semiconductors have the drawbacks of inferior material workability and expensiveness.
Therefore, relatively inexpensive oxidized compound semiconductors which easily achieve good material workability have been attracting attention recently, and research and development of ultraviolet sensors which have a p-type semiconductor layer and an n-type semiconductor layer joined in the form of a hetero junction by using these oxidized compound semiconductors have been actively carried out.
For example, Patent Document 1 proposes, as shown in FIG. 11, an ultraviolet sensor including a (Ni, Zn)O layer 101 composed of an oxidized compound semiconductor which has a solid solution of ZnO in NiO, a thin-film material layer 103 formed by a sputtering method so as to cover a portion of one principal surface 102 of the (Ni, Zn)O layer 101, and first and second terminal electrodes 104a, 104b formed on both ends of the (Ni, Zn)O layer 101, where an internal electrode 105 is formed in the (Ni, Zn)O layer 101, and the first terminal electrode 104a is electrically connected to the internal electrode 105, whereas the second terminal electrode 104b is electrically connected to the thin-film material layer 103.
In Patent Document 1, the internal electrode 105 has one end electrically connected to the terminal electrode 104a, and the other end formed to extend substantially to the center in the (Ni, Zn)O layer 101. In addition, the thin-film material layer 103 is provided to be opposed to the internal electrode 105, and formed to have a partial overlap with the internal electrode 105 in planar view, and the thin-film material layer 103 is connected to the other terminal electrode 104b. 
Further, in Patent Document 1, when ultraviolet irradiation is performed from above in the figure to expose a depletion layer formed at the joint interface between the (Ni, Zn)O layer 101 and the thin-film material layer 103 to the ultraviolet light, carriers are excited to generate photovoltaic power in an overlap a between the thin-film material layer 103 and the internal electrode 105.
Patent Document 1: JP 2010-87482 A (claim 1, FIG. 1)